Abstract 270: Role of the Mitochondrial Iron in Cardiomyoblast Survival and Maturation of Cytosolic Fe/S Proteins.

Abstract

ATP-binding cassette (ABC)-B8 is an ABC half transporter that resides in the inner mitochondrial membrane. We previously showed that ABCB8 has a role in mitochondrial iron export, and that a reduction in ABCB8 both in vitro and in vivo results in mitochondrial iron accumulation, increased reactive oxygen species (ROS) and cell death, and decreased activity of cytosolic Fe/S proteins. However, it is not known whether the cytotoxic effects of ABCB8 knockdown are due to mitochondrial iron accumulation or decreased cytosolic Fe/S protein or other processes. Furthermore, the link between mitochondrial iron and the activity of cytosolic Fe/S proteins is uncharacterized. Here, we studied whether a reduction in mitochondrial iron can reverse the effects of ABCB8 knockdown on cell survival, ROS production and the activity of Fe/S proteins. We altered the mitochondrial iron using various iron chelators and by decreasing the levels of mitochondrial iron importer, mitoferrin-2 (MFRN2). The increase in mitochondrial iron and ROS levels associated with ABCB8 knockdown was significantly reversed by iron chelators and with MFRN-2 knockdown. Furthermore, cell death was also reversed with iron chelators and MFRN-2 knockdown, suggesting that the cytotoxic effects of ABCB8 knockdown is due to mitochondrial iron accumulation. We then studied the effects of iron chelators on cytosolic Fe/S proteins. Iron chelators reversed the defect in cytosolic Fe/S proteins that is associated with ABCB8 knockdown in cell culture or knockout in mice. However, antioxidants and knockdown of MFRN-2 failed to have similar effects. These results indicated that the defect in the maturation of cytosolic Fe/S proteins due to mitochondrial iron accumulation can be reversed by chelating mitochondrial iron, and is independent of the associated oxidative stress. Thus, mitochondrial iron levels are likely sensed in the cytoplasm and determine the maturation of cytosolic Fe/S proteins. Altogether, these studies provide insights into the role of mitochondrial iron in the cytotoxic effects of ABCB8 knockdown, and suggest that mitochondrial iron is sensed in the cytoplasm and influences the maturation of cytosolic Fe/S proteins.